test_load_set_dpi fails on Windows with 7.1.2

[hugovk]

====================================================================== test session starts =======================================================================
platform win32 -- Python 3.8.2, pytest-5.4.1, py-1.8.1, pluggy-0.13.1 -- X:\Python38\python.exe
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('D:\\Build\\Pillow\\Pillow-7.1.2\\.hypothesis\\examples')
--------------------------------------------------------------------
Pillow 7.1.2
Python 3.8.2 (tags/v3.8.2:7b3ab59, Feb 25 2020, 23:03:10) [MSC v.1916 64 bit (AMD64)]
--------------------------------------------------------------------
Python modules loaded from X:\Python38\lib\site-packages\PIL
Binary modules loaded from X:\Python38\lib\site-packages\PIL
--------------------------------------------------------------------
--- PIL CORE support ok
--- TKINTER support ok
--- FREETYPE2 support ok
--- LITTLECMS2 support ok
--- WEBP support ok
--- WEBP Transparency support ok
--- WEBPMUX support ok
--- WEBP Animation support ok
--- JPEG support ok
--- OPENJPEG (JPEG2000) support ok
--- ZLIB (PNG/ZIP) support ok
--- LIBTIFF support ok
--- RAQM (Bidirectional Text) support ok
*** LIBIMAGEQUANT (Quantization method) support not installed
*** XCB (X protocol) support not installed
--------------------------------------------------------------------

rootdir: D:\Build\Pillow\Pillow-7.1.2, inifile: setup.cfg
plugins: hypothesis-5.10.4, palladium-1.2.2, cov-2.8.1, forked-1.1.3, xdist-1.31.0
collected 1456 items

Tests/test_000_sanity.py::test_sanity PASSED                                                                                                                [  0%]
<snip>
Tests/test_webp_leaks.py::TestWebPLeaks::test_leak_load SKIPPED                                                                                             [100%]

============================================================================ FAILURES ============================================================================
_______________________________________________________________________ test_load_set_dpi ________________________________________________________________________

    def test_load_set_dpi():
        with Image.open("Tests/images/drawing.wmf") as im:
            assert im.size == (82, 82)

            if hasattr(Image.core, "drawwmf"):
                im.load(144)
                assert im.size == (164, 164)

                with Image.open("Tests/images/drawing_wmf_ref_144.png") as expected:
>                   assert_image_similar(im, expected, 2.0)

Tests\test_file_wmf.py:69:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Tests\helper.py:140: in assert_image_similar
    raise e
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

a = <PIL.Image.Image image mode=RGB size=164x164 at 0x21B0019A4F0>, b = <PIL.PngImagePlugin.PngImageFile image mode=RGB size=164x164 at 0x21B0019A1F0>
epsilon = 2.0, msg = None

    def assert_image_similar(a, b, epsilon, msg=None):
        assert a.mode == b.mode, msg or "got mode {!r}, expected {!r}".format(
            a.mode, b.mode
        )
        assert a.size == b.size, msg or "got size {!r}, expected {!r}".format(
            a.size, b.size
        )

        a, b = convert_to_comparable(a, b)

        diff = 0
        for ach, bch in zip(a.split(), b.split()):
            chdiff = ImageMath.eval("abs(a - b)", a=ach, b=bch).convert("L")
            diff += sum(i * num for i, num in enumerate(chdiff.histogram()))

        ave_diff = diff / (a.size[0] * a.size[1])
        try:
>           assert epsilon >= ave_diff, (
                msg or ""
            ) + " average pixel value difference %.4f > epsilon %.4f" % (ave_diff, epsilon)
E           AssertionError:  average pixel value difference 2.0669 > epsilon 2.0000
E           assert 2.0 >= 2.0668500892325996

Tests\helper.py:130: AssertionError
---------------------------------------------------------------------- Captured stdout call ----------------------------------------------------------------------
STREAM b'IHDR' 16 13
STREAM b'IDAT' 41 1152
----------------------------------------------------------------------- Captured log call ------------------------------------------------------------------------
DEBUG    PIL.PngImagePlugin:PngImagePlugin.py:153 STREAM b'IHDR' 16 13
DEBUG    PIL.PngImagePlugin:PngImagePlugin.py:153 STREAM b'IDAT' 41 1152
======================================================================== warnings summary ========================================================================
Tests/test_file_wmf.py::test_load_raw
Tests/test_file_wmf.py::test_load_raw
Tests/test_file_wmf.py::test_load_set_dpi
  X:\Python38\lib\site-packages\PIL\WmfImagePlugin.py:51: DeprecationWarning: PY_SSIZE_T_CLEAN will be required for '#' formats
    Image.core.drawwmf(im.fp.read(), im.size, self.bbox),

Tests/test_imagewin.py::TestImageWinDib::test_dib_frombytes_tobytes_roundtrip
  X:\Python38\lib\site-packages\PIL\ImageWin.py:178: DeprecationWarning: PY_SSIZE_T_CLEAN will be required for '#' formats
    return self.image.frombytes(buffer)

-- Docs: https://docs.pytest.org/en/latest/warnings.html
==================================================================== short test summary info =====================================================================
SKIPPED [1] Tests\test_file_gif.py:221: Netpbm not available
SKIPPED [1] Tests\test_file_gif.py:232: Netpbm not available
SKIPPED [1] Tests\test_file_icns.py:28: Requires macOS
SKIPPED [1] Tests\test_file_icns.py:41: Requires macOS
SKIPPED [1] Tests\test_file_msp.py:58: Extra image files not installed
SKIPPED [1] Tests\test_file_msp.py:72: Even More Extra image files not installed
SKIPPED [1] D:\Build\Pillow\Pillow-7.1.2\Tests\helper.py:170: Palm P image is wrong
SKIPPED [1] Tests\test_file_png.py:650: Requires Unix or macOS
SKIPPED [1] Tests\test_file_sun.py:35: Extra image files not installed
SKIPPED [1] Tests\test_font_leaks.py:20: Requires Unix or macOS
SKIPPED [1] Tests\test_font_leaks.py:31: Requires Unix or macOS
SKIPPED [1] Tests\test_image.py:166: Test requires opening tempfile twice
SKIPPED [1] D:\Build\Pillow\Pillow-7.1.2\Tests\test_image_quantize.py:25: libimagequant support not available
SKIPPED [1] D:\Build\Pillow\Pillow-7.1.2\Tests\test_imagedraw.py:784: failing
SKIPPED [2] Tests\test_imagefont.py:483: requires Unix or macOS
SKIPPED [2] Tests\test_imagefont.py:524: requires Unix or macOS
SKIPPED [1] Tests\test_imagegrab.py:25: requires XCB
SKIPPED [1] Tests\test_imagegrab.py:48: requires XCB
SKIPPED [1] Tests\test_imageshow.py:40: Only run on CIs; hangs on Windows on GitHub Actions
SKIPPED [1] Tests\test_map.py:11: Win32 does not call map_buffer
SKIPPED [1] Tests\test_map.py:29: Win32 does not call map_buffer
SKIPPED [1] Tests\test_shell_injection.py:24: Requires Unix or macOS
SKIPPED [1] Tests\test_shell_injection.py:33: Requires Unix or macOS
SKIPPED [1] Tests\test_shell_injection.py:38: Netpbm not available
SKIPPED [1] Tests\test_shell_injection.py:44: Netpbm not available
SKIPPED [1] Tests\test_webp_leaks.py:16: Requires Unix or macOS
==================================================== 1 failed, 1427 passed, 28 skipped, 4 warnings in 28.06s =====================================================

Originally posted by @cgohlke in #4354 (comment)